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Reliability assessment of ductile frame structures in a systematic manner has remained a challenging issue because of the difficulties in searching for important failure modes and evaluating the system probability of failure stemmed from these important modes. In this paper, based on the Box-Cox transformation, a new failure mode independent performance function with the probability distribution of weak non-normality is proposed for the system reliability assessment of ductile frame structures. An efficient approach is then developed for estimating the failure probability of the proposed performance function, which includes two steps: first, the point-estimate method based on hybrid dimension-reduction integrated with structural limit analysis is developed to evaluate the first four central moments (i.e., mean, standard deviation, skewness, and kurtosis) of the proposed performance function; next, the system probability of failure corresponding to the proposed performance function is then estimated using the moment-based reliability method. Three numerical examples are presented to demonstrate the efficiency and accuracy of the proposed method, where the method of subset simulation is employed for comparison. It can be concluded that the developed methodology successfully overcomes the two difficulties including the identification of important failure modes and the evaluation of system probability of failure stemmed from these important modes in system reliability assessment of ductile frame structures.

Mechanical heterogeneity is a major characteristic of the organic-rich shale. The relation between mechanical heterogeneity and formation in-situ stress has been seldomly addressed but important to understand hydraulic fracture propagation, wellbore stability, and hydrocarbon flow. In this paper, the grid nanoindentation technique was used to characterize the heterogeneity of the mechanical properties of Longmaxi organic-rich shales from various burial depths and in-situ stress. The measured elastic modulus and hardness of each sample are deconvolved into three phases including soft phase, medium stiff phase and stiff phase according to mineral category. As the burial depth and corresponding in-situ stress increase, the overall elastic modulus and hardness of the sample enhance. Simultaneously, the percentage of soft minerals decreases, and the probability distribution tends to concentrate through 95% confidence interval evaluation which demonstrates weakened heterogeneity. Furthermore, SEM images provide evidence that extended cracking, initiated cracking, crushing and ductile deforming always occur around indentation imprints. This confirms that even under deep buried depth and high in-situ stress, brittle fracture and ductile deformation can exist synchronously. This paper demonstrates the influence of in-situ stress on the heterogeneity of shale micromechanics.

On-site observations show that several damages have occurred in CRTS II slab-type ballastless track system, such as crack and interface debonding between different structural layers, which will trigger the occurrence of some failure modes of CRTS II track slab. As the damages are the prior for specific failure modes, time-dependent reliability of CRTS II track slab should be conducted considering the uncertainties associated with both the failure mode and the damage, which is defined as the conditional time-dependent reliability in this study. To appropriately express the causal relationship among the failure modes and prior damages, a conditional limit state function (LSF) model is proposed with explicit expressions provided. With the aid of the proposed model, conditional time-dependent reliability of CRTS II track slab for two individual failure modes are investigated, which are the steel yielding failure mode under longitudinal cracking, and the vertical instability failure mode under interface debonding. Furthermore, conditional time-dependent system reliability of the track slab has also been analyzed considering four safety failure modes. The advantage of the proposed method is that prior damages have been accounted in establishing the failure criteria and incorporated in the formulation of time-dependent reliability, which provides a general formwork for structural reliability involving the causal relationship among the failure modes and damages.

The service life of reinforced concrete structures is significantly affected by the chloride-induced corrosion of reinforcing steel. This paper presents a comprehensive study on the influence of the corrosion environment and other parameters on the corrosion rate of reinforcing steel in concrete. Comparative tests were carried out on concrete block and beam specimens subjected to accelerated corrosion in indoor and outdoor environments for a period of 1.5 years. The experimental variables considered included the chloride content, depth of concrete cover, type of reinforcing steel and water-to-cement (w/c) ratio. The test results indicated that the corrosion rate of the reinforcing steel increases with the increase in the w/c ratio, chloride content, temperature and relative humidity, while it is reduced when the thickness of the concrete cover increases. Furthermore, an empirical model for predicting the corrosion rate of reinforcing steel in concrete is proposed using the experimental data, which offers a good prediction of the corrosion rate.

In this paper, a total of 70 experimental flexural tests of corroded post-tensioned prestressed concrete (PC) beams were gathered from the published literatures. Using the experimental data, a comprehensive databank of flexural capacity of the corroded PC beams was established. Meanwhile, four existing empirical models for calculating the residual flexural strength of the corroded PC beams were also gleaned and contrasted with each other based on the databank. It turns out that three of the four existing empirical models underestimate the flexural capacity. To deeply analyze the factors affecting the flexural capacity, numerous factors were discussed, e.g., the corrosion ratio, beam width, effective height of the beam section, concrete compressive strength, and the ratio of strength between the tensile reinforcement (including prestressed and non-prestressed reinforcement) and concrete. It is found that the corroded post-tensioned PC beams’ residual flexural capacity is affected most by the corrosion ratio. In the end, a better empirical model is proposed for computing the residual flexural capacity of corroded PC beams, which provides accurate and effective predictions in a wide range of corrosion ratio for engineering practice.

The interface damage is one of the main concerns for high-speed railway ballastless track structures during its whole service life, as it would affect the reliability of track structures or even cause the high-speed train accident. In this paper, various existing cohesive zone models (CZMs) were identified and compared regarding the performance in modeling the interface behaviors of ballastless track structures. The results show that the existing CZMs cannot accurately represent the nonlinear relationship of the ascending and descending sections in the interface traction-separation curve concurrently. Therefore, a new CZM was proposed in this study, and the feasibility of the proposed model was examined by the experimental results. It indicates that the proposed model can reasonably describe the nonlinear behaviors of the ascending and descending sections in the traction-separation curve by introducing exponential coefficients. The proposed CZM also exhibits higher accuracy in predicting the normal and tangential cracking behaviors of the interlayer interface of the ballastless track structures in comparison with the existing models, with the coefficients of determination (R2) in the fitting results all above 0.85. As a result, this model can be used for the analysis of the interface behaviours of ballastless track structures.

Background The interaction between tumor microenvironment (TME) and tumors offers various targets in mounting anti-tumor immunotherapies. However, the prognostic biomarkers in endometrial carcinoma (EC) are still limited. Here, we aimed to analyze the TME features and identify novel prognostic biomarkers for EC. Methods ESTIMATE, CIBERSORT, protein-protein interaction (PPI) network, univariate and multivariate Cox regression, and functional enrichment analysis were performed to identify immune- and survival-related hub genes as well as possible molecular mechanisms. The limma package and deconvolution algorithm were adopted to estimate the abundance of tumor-infiltrating immune cells (TICs) and their relationship with the target gene. In the validation section, tissue microarrays (TMAs) of EC and multiplex immunohistochemistry (m-IHC) were evaluated to validate the expression of TNFRSF4, and its correlation with immune markers, including CD4, CD8, and FOXP3. Besides, the receiver operating characteristic (ROC) curve was plotted to determine the diagnostic performance of TNFRSF4, CD4, CD8, and FOXP3 in EC. Results Two genes, TNFRSF4 and S1PR4, were screened out from 386 intersection differential expression genes (DEGs) shared by ImmuneScore and StromalScore in EC. Highlighted by TNFRSF4, we found that it was not only positively correlated with the TICs (mainly CD4+ T cells, CD8+ T cells, and Tregs) but significantly related to the prognosis in patients of EC, both verified by data from The Cancer Genome Altas (TCGA)-EC database and clinical samples. At the same time, the expression trend of TNFRSF4 was further confirmed by an integrated meta-analysis based on six microarrays from the Gene Expression Omnibus database (GEO). Conclusions Collectively, TNFRSF4, a previously unrecognized key player in EC, could serve as a potential biomarker for prognosis prediction and immunomodulation of EC.

Bayesian updating of the reliability of deteriorating engineering structures based on inspection data has been attracting a lot of attention recently because it can provide more accurate es...

The existing theoretical models for the analysis of concrete-filled steel tube (CFST) columns are mainly limited to circular specimens. This paper is aimed at developing a unified theoretic...

The concept of system reliability will be described in this chapter. A moment-based method for assessing the system reliability of series and non-series structures is investigated, with emphasis on series systems. The reliability index is directly calculated based on the first few moments of the system performance function of a structure. It requires neither the reliability analysis of the individual failure modes nor the iterative computation of derivatives, the computation of the mutual correlations among the failure modes, and any design points. As a practical topic, the evaluation of system reliability for ductile frame structures using methods of moment is introduced in the final part of this chapter. The difficulty in both failure mode identification and failure probability computation is still hard to overcome when using the traditional method for the system reliability assessment of ductile frame structures. To avoid the difficulties, a failure mode independent performance function with weak non-normality is introduced. The method of moments is then utilized to estimate the failure probability of ductile frame structures corresponding to the general performance function. From the numerical examples, it can be concluded that the introduced methodology successfully overcomes the two difficulties including the identification of significant failure modes and the computation of overall failure probabilities contributed from these significant modes in system reliability evaluation of ductile frame structures.

Evaluating the failure probabilities with rare events remains a challenging task, especially when dealing with complex limit state functions with high-dimensional random inputs. To handle this problem, an adaptive polynomial skewed-normal transformation (A-PSNT) model is proposed in this paper for evaluating the probability distribution of the limit state function and failure probability. First, the polynomial transformation models on the basis of normal distribution are introduced, where the limitations are also pointed out. Then, the skewed-normal distribution is presented, which serves as the basis of the proposed polynomial transformation model. The PSNT with a given order can be initiated, whereby the unknown coefficients can be determined by using the probability weighted moments (PWMs)-matching technique. Further, a tail error criterion is proposed to select the most appropriate order for the PSNT model, which makes the proposed method an adaptive one. To handle the low- to high-dimensional random inputs, two low-discrepancy sampling methods are employed to generate samples for unbiasedly estimating the PWMs of the limit state function. Once the probability distribution of the limit state function is reconstructed by the proposed A-PSNT model, the failure probability, especially for the rare one, can be determined accordingly. The proposed method is validated through numerical examples involving both static and dynamic, low- to high-dimensional problems, where some classical reliability analysis methods are also adopted for comparisons. The results show that the proposed A-PSNT model not only can effectively reconstruct the probability distribution, but also is able to accurately predict the failure probability with rare events.

This paper proposes a new method for seismic fragility analysis of nuclear power plants (NPPs) considering the uncertainty sources of both ground motions and structural parameters. Based on the conventional seismic fragility model that only contains the uncertainty of ground motions, seismic fragility analysis conditioned on a specific seismic intensity is probabilistically reformulated by further incorporating the uncertainty of structural parameters. To improve the efficiency of the analysis, a point estimation-assisted incremental dynamic analysis was developed for evaluating the seismic fragility model including the uncertainty of structural parameter. The accuracy and efficiency of the proposed method were demonstrated by a single-degree-of-freedom system, where Monte Carlo simulation method is used for comparison. The seismic fragility based on the finite element model of an AP1000 NPP was analyzed using the proposed method. The results reveal that the safety of NPP structure would be overestimated without considering the uncertainty of structural parameter and the influence of the uncertainty of structural parameters on the seismic fragility of NPP presents an upward trend as the damage level increases. Furthermore, the sensitivity analysis of different structural parameters reveals that elastic module may have a dominant influence.

Analyzing the uncertainty of flutter propagated from different sources especially flutter derivatives is important for the risk assessment of long-span bridges. The uncertainty of flutter derivatives is often characterized based on the experimental data. Dependence and sampling error would therefore exist which may influence the onset prediction of bridges. This paper devotes to developing a framework towards the uncertainty analysis of bridge flutter considering the dependence and sampling error in flutter derivative measurements. In this framework, the dependence among different flutter derivatives is identified with Spearman’s rho instead of conventional Pearson’s product-moment correlation coefficient. A modified procedure based on bootstrap is proposed to characterize the sampling error by representing distribution parameters of flutter derivatives as interval variables. Regarding the probability-interval hybrid uncertainty, a double-layer analysis is employed. In the inner layer, probability of onset velocity is estimated using the point estimate-based probability analysis. In the outer one, the distribution envelope is obtained by the genetic algorithm-assisted interval analysis. Application of the framework to reliability assessment of bridge against flutter is also presented. In the numerical study, the influence of dependence and sampling error is verified in detail. By this framework, the distribution envelope of onset velocity or the interval of reliability index against flutter are expected to contain the true estimates. Consequently, the potential risk with respect to bridge flutter can be assessed in a conservative way.